Strong, defined abs don't require high-impact activity. Stay grounded on a mat or your own two feet and effectively train all the muscles of your belly. In 2001, the American Council on Exercise rated a number of ab exercises for their effectiveness. The best ones are all not only low-impact — they are no impact.
The basic crunch is a staple ab exercise that trains the rectus abdominis, the front sheath of your abs. It's inherently low-impact, but the basic version may not be the most impactful. Do the crunch with extended legs or on a stability ball for most effect.
1. Stability Ball Crunches
HOW TO DO IT: Lie on a stability ball so your low-back is anchored to the ball and your thighs and feet are parallel with the floor. Cradle your head with your hands or cross your arms over your chest.
Draw your abdominal muscles in toward your spine as you raise your head, neck and shoulders up to about a 45-degree angle. Lower to the start to complete one repetition.
To make the exercise more challenging, bring your feet close together. For greater stability, widen the legs.
2. Long-Leg Crunch
HOW TO DO IT: Lie on your back on a mat and cradle your head with your hands. Extend your legs straight toward the ceiling. Keep them positioned straight over your hips.
Exhale as you lift your torso up to crunch your chest toward your legs. Pull your abdominal muscles in tightly as you lift.
Avoid tugging on the back of your head or pulling your chin to your chest.
Read more: 21 Sit-up Variations You Won't Totally Hate
Crunches alone don't target all of the muscles of the core. Planks train the deep transverse abdominis, which helps you stand tall and boosts balance. The classic plank has your torso suspended on your hands or forearms and toes.
Hold your body rigid, with the belly button pulled in toward the spine, for 20 to 90 seconds as a time. Once you master the basic version, add challenge with other options.
1. Side Plank
HOW TO DO IT: Start in plank position on your hands or forearms. Bring your feet together and lean to the right side so you stack your feet and hips in one line.
Lift your left arm straight up to the ceiling. Hold side plank for 20 to 90 seconds. Switch sides for balanced muscle development.
If you find it too hard to balance on your stacked feet and arm, lower the bottom knee to the floor but keep lifting up through the hips. This modification helps you build strength with good form.
2. Balancing Planks
HOW TO DO IT: Get into regular plank position on your toes and hands/forearms and extend one arm forward for three to five counts. Lower it back to the floor and repeat with the opposite side.
From regular plank, lift one leg for three to five counts. Lower it down and repeat with the other side. From regular plank, reach your right arm forward and your left leg off the floor for three to five counts. Repeat with the left arm and right leg.
Place your hands or forearms on a stability ball or balancing disc while you hold plant. Alternatively, put your feet on the balancing device.
Twisting movements train the obliques that exist at the sides of your waist. These muscles help give you a completely defined look and support functional movement, such as rotating and side bending.
1. Medicine Ball Twist
HOW TO DO IT: Get into seated position on a mat. Bend your knees and plant your feet flat on the floor. Hold a 2- to 15-pound medicine ball in both hands in the center of your chest.
Lean back slightly so you feel your abdominal muscles contract. Rotate your entire torso to the right, bringing the ball with you and then rotate to the left.
Increase intensity by lifting your feet off the floor so the toes are just an inch up. For even more effort, left the legs with the knees bent and the shins parallel to the floor. A final variation has you in a full v-sit with the legs extended at about 45 degrees.
2. Bicycle Crunches
HOW TO DO IT: Lie on your back on a mat and cradle your head with your hands. Draw your legs up so you form a 90-degree angle at your hips and knees, with your shins parallel to the floor.
Extend your right leg straight out as you pull your right armpit and elbow and left knee closer together. Switch sides. Move fluidly as if you were pedaling a bike.
Avoid holding your breath during any of these moves. Inhale and exhale naturally.
Read more: 12 Moves for a Stronger Core and Better Posture